1. Field of the Invention
The present invention relates to a color picture tube apparatus used in a television, a computer display, or the like. Furthermore, the present invention relates to a deflection yoke and a ferrite core used in the color picture tube apparatus.
2. Description of the Related Art
In order to reduce the required deflection power and suppress the heat generated by a deflection yoke, JP61(1986)-56757U discloses a so-called slot core in which a plurality of convex portions protruding toward a tube axis of a picture tube are provided on an inner surface of a ferrite core constituting a deflection yoke. FIG. 17 shows a cross-sectional view of the deflection yoke with the slot core, taken along a surface vertical to the tube axis at a position close to an electron gun. As shown in FIG. 17, a tube axis of the picture tube on which the deflection yoke is mounted is a Z-axis, a horizontal axis orthogonal to the Z-axis is an X-axis, and a vertical axis orthogonal to the Z-axis and the X-axis is a Y-axis. In FIG. 17, reference numeral 90 denotes a ferrite core, and 91 denotes a plurality of convex portions provided on an inner surface of the ferrite core 90. Windings are inserted in grooves between the convex portions 91 adjacent to each other in a circumferential direction, whereby a horizontal deflection coil 97 and a vertical deflection coil 98 are wound therein. Reference numeral 99 denotes an insulating frame for insulating the horizontal deflection coil 97 from the vertical deflection coil 98. Each convex portion 91 extends over the entire region in a tube axis direction from an end on an electron gun side of the ferrite core 90 to an end on a screen side thereof, along a plane that includes the tube axis. By providing such convex portions 91, compared with the case where the convex portions 91 are not provided, the ferrite core 90 can be brought close to the picture tube. Therefore, the deflection efficiency can be enhanced, which is advantageous for reducing a deflection power. Furthermore, since a magnetic flux is unlikely to cross the coils 97, 98, an eddy current loss is reduced, and the heat generated by the deflection yoke also can be decreased.
The deflection yoke is mounted on an outer circumferential surface of a funnel of the color picture tube. The cross-sectional shape of the outer circumferential surface of the funnel in a portion where the deflection yoke is mounted, taken along a surface vertical to the tube axis, generally used to be circular in a conventional example. However, a funnel has come to be used in which the cross-sectional shape of a diameter-changing portion is varied gradually from a circular shape to a substantially rectangular shape in a direction from a neck side to a phosphor screen side, except for the neck in which an electron gun is housed, so as to be matched with a rectangular display screen on which a phosphor screen is formed. In order to accommodate this configuration, as shown in FIG. 18, a deflection yoke is proposed, in which each cross-sectional shape of the ferrite core 90, the horizontal deflection coil 97, the vertical deflection coil 98, and the insulating frame 99 is set to be substantially rectangular (e.g., see International Publication No. WO 99/26270). In this deflection yoke, an envelope-curve 94 connecting tip ends of the convex portions 91 formed on the inner circumferential surface of the ferrite core 90 also is substantially rectangular. Thus, by setting the cross-sectional shape of each component constituting the deflection yoke to be substantially rectangular in accordance with the cross-sectional shape of the outer circumferential surface of the substantially rectangular funnel, the deflection yoke, in particular, the convex portions 91 of the ferrite core 90 can be brought close to an electron beam. Therefore, the deflection sensitivity is enhanced further, and the deflection power can be reduced further.
Furthermore, JP2004-14349A proposes a deflection yoke as shown in FIG. 19. This deflection yoke is different from that shown in FIG. 18 in that the cross-sectional shape on an XY-plane of the inner circumferential surface of the ferrite core 90 excluding the convex portions 91 (smooth virtual curved surface obtained by successively connecting bottom surfaces of grooves between the convex portions 91) and the cross-sectional shape on the XY-plane of the outer circumferential surface of the ferrite core 90 are both circular. The envelope curve 94 connecting the tip ends of the convex portions 91 is substantially rectangular so as to be matched with the cross-sectional shape of the outer circumferential surface of a funnel on which the deflection yoke is to be mounted. Thus, in the deflection yoke shown in FIG. 19, the deflection sensitivity can be enhanced, and the deflection power can be reduced, in the same way as in the deflection yoke shown in FIG. 18.
Furthermore, the ferrite core 90 used in the deflection yoke shown in FIG. 19 has a circular cross-sectional shape on the XY-plane, except for the envelope curve 94 connecting the tip ends of the convex portions 91. Therefore, the ferrite core 90 shown in FIG. 19 can be designed more easily and has more satisfactory size stability, compared with the ferrite core 90 used in the deflection yoke shown in FIG. 18.
Furthermore, in a process of sintering a ferrite core, the ferrite core 90 shown in FIG. 19 has an advantage compared with that shown in FIG. 18. The reason for this is as follows. When a ferrite core is sintered, an uncured ferrite core needs to be held by a mortar-shaped fixing jig having an opening, which can come into contact with the outer circumferential surface of the ferrite core over the entire circumference. Regarding the ferrite core shown in FIG. 18, a dedicated fixing jig matched with the outer circumferential surface of the substantially rectangular cross-section is required. In contrast, regarding the ferrite core shown in FIG. 19, irrespective of the outer diameter of the ferrite core, a general-purpose common fixing jig having a substantially circular conical surface can be used. Furthermore, since a common fixing jig can be used, the heat capacity of the fixing jig becomes the same, and even in the case of sintering a plurality of kinds of ferrite cores simultaneously, it is easy to set sintering conditions. Thus, in the ferrite core shown in FIG. 19, the sintering process can be performed efficiently at a low cost. Furthermore, the number of fixing jigs accommodated in a sintering furnace also can be kept constant with a satisfactory efficiency.
However, in the ferrite core shown in FIG. 19, irrespective of the position in the tube axis direction, each cross-sectional shape of the inner circumferential surface excluding the convex portions 91 and the outer circumferential surface is circular, whereas the envelope curve 94 connecting the tip ends of the convex portions 91 is substantially rectangular. Therefore, when the tip ends of the convex portions 91 are brought close to the outer circumferential surface of the funnel, the protrusion length of the convex portions 91 becomes large, and the convex portions 91 become chipped, whereby the yield in the course of production of a ferrite core decreases.